Depression of ad lib and angiotensin-induced sodium intake at oestrus

During the rat oestrous cycle, cholinergic-stimulated water intake is constant across days; while both daily ad lib and angiotensin II-stimulated water intakes are least on the day of oestrus. If permitted to self select, however, rats will elect to drink sodium chloride solutions as well as water under ad lib or angiotensin-stimulated conditions. Therefore, adult female rats with continuous access to both water and 1.8% NaCl were studied to determine if saline intake also varied with the oestrous cycle. Ad lib drinking and drinking stimulated by intracerebroventricular injections of angiotensin II or carbachol were monitored daily for the duration of an entire oestrous cycle. Both ad lib and angiotensin-induced sodium intakes were depressed at oestrus, while the minimal sodium intake seen after carbachol was not changed. The depression in sodium intake so mirrored that observed for water intake that the ratio of saline to water intake did not vary over the oestrous cycle.